In recent years, the use of wireless and microwave technology has increased dramatically in consumer applications as well as commercial applications. This has resulted in a proliferation of portable and hand-held units, where such units are deployed by a variety of individuals from soldiers on the battlefield to mothers contacting their children. The uses of wireless and microwave technology are widespread, increasing, and include but are not limited to radio, telephony, Internet e-mail, Internet web browsers, global positioning, wireless computer peripherals, wireless networks, security tags and in-store navigation.
Within any microwave circuit using microwave signals there is a highly sensitive chain of microwave electronics providing both the transmission and receiver functions. These microwave circuits generally necessitate not only direct manipulation of the microwave signal, for example by amplification, attenuation, mixing or detection, but also ancillary functions such as power monitoring, signal identification, and control. Additionally these functions may be undertaken post mixing, such that the signals are at a lower frequency, typically referred to as Intermediate Frequency (IF), than the original received signal. The latter includes, for example, the extraction of modulated information for radio, telephony, data or video signals from their carriers in wireless or satellite networks, to inventory management with RFID, and analog signal identification and analysis from microwave carriers in military applications such as missile threat detection.
In the manufacturing of devices for these applications there are continued demands for lower cost, increased performance, increased volume and enhanced flexibility from the microwave circuits. These demands have resulted in a wide range of microwave circuits, both those built from discrete elements or those using monolithic microwave integrated circuits. Additionally the leveraging of semiconductor manufacturing approaches has resulted in suppliers of microwave circuits who have their own manufacturing operations-fabrication facility (Fab) and those who access commercial manufacturing operations (Foundry) and are known as Fabless operations. Fabless operations therefore are generally designing to a pre-defined manufacturing process flow with defined tolerances and constraints, typically referred to as design rules. For example, IBM offers foundry access for RF CMOS products with three sets of design rules CMOS 6RF©, CMOS 7RF©, and CMOS 8RF©. These are based upon three different lithography processes, 250 nm, 180 nm and 130 nm respectively, along with design, metallization and layout rules.
In many instances the Fabless companies are accessing Foundry operations of a corporation having its own fabrication facility and offering products within similar markets. Typically, the external Fabless businesses access the Foundry with an older set of design rules, whereas the Foundry's internal groups access newer improved rules, processes, as well as being allowed to breach layout design rules for improved performance, lower cost and increased competitive edge.
It is well know to those skilled in the art that for either internal designer or Fabless based designer that the run to run variances in the manufacturing processes of the semiconductor facility result in variations of many basic parameters of the circuits as well as the underlying qualities of the technology elements such as transistors, resistors, capacitors and inductors. Such technology elements are considered the elemental devices of the semiconductor technology. It is not uncommon for Fabless design rules to set tolerances of ±25% to a resistor value for a specific process on their older design rules. Thus, a resistor implemented in the circuit with an intended value of 100 Ohms might be as low as 75 Ohms or as high as 125 Ohms in one or more lots of the final manufactured circuit. The result of the resistor tolerance is that the manufactured product on a set of design rules has a distribution around the nominal design value. As basic microwave device elements, such as transistors, move away from their nominal design point, critical performance characteristics might degrade such as gain, output power, linearity, noise figure, and bandwidth.
A designer working with these design rules must either design a product that works to specification over the full tolerance range, thereby having a high yield but with a reduced specification, or accept a reduced yield with improved specification. This is a trade-off that is well known in the art of circuit design. For microwave circuits, the manufacturing variations requires the functional testing of the microwave circuit to decide whether the part has passed or failed to fulfill the component specification. In fact, the common practice of offering two or more specifications for a product is an attempt by a business to generate additional revenue for parts at lower specifications.
For monolithic microwave integrated circuits (MMICs), it is also well known to those skilled in the art that the approximately optimal bias voltage for a transistor, the core building block of many MMICs such as amplifiers and attenuators, varies with the exact semiconductor materials, semiconductor processes employed in manufacturing and the resulting device geometry and parameters. Within semiconductor manufacturing these parameters vary even across a single wafer, which can contain hundreds to thousands of microwave circuit die. Hence, even a single wafer results in a distribution of performance around a median value. If this median is sufficiently far from the nominal design point for a designer working with reduced tolerances against a Foundry process, then the result may be that the yield of that entire wafer, or that entire batch of wafers of several tens of thousands of parts might be zero or extremely low causing the business supply issues and customer dissatisfaction.
It is advantageous therefore in reaching a design with high performance and low cost for the effective design range of the Foundry process to be reduced. It is known that whilst within a single wafer every transistor, for example, has a discrete optimal operating point that varies according to the transistors position within the wafer, these variations are gradual and that typically therefore for a monolithic microwave integrated circuit each die has a significantly reduced variation.
It is known from prior art to exploit the dependence of the performance of the microwave circuit on bias point and individually tune every microwave circuit for bias voltage such that the circuits operate from a single specified power supply, thereby eliminating the cost to the device user of tuning the imperfect manufacturing out. Such an approach is typically accomplished through the use of laser trimming in a resistive divider network within the microwave circuit. The derivation of the optimal setting of the resistive divider made from the microwave characterization of the microwave circuit. This step requiring not only time and labor but also significant expenditure in complex microwave test instruments.
It would be advantageous, to derived the optimal settings from information requiring reduced time, labor and eliminating complex and expensive microwave test equipment. Further, it would be advantageous if the manufacturer could use the information to adjust multiple control settings within the microwave circuit such that it meets the desired exacting specification without reduced yield. Finally it would be advantageous if the adjustment of the necessary control settings were performed by the circuit automatically.